The present invention relates to a piezoelectric element formation member comprising piezoelectric material layer which are deformable in accordance with the application of voltages, and a method of manufacturing such a piezoelectric element formation member. The present invention also relates to a piezoelectric actuator unit in which piezoelectric elements are arrayed and integrated with each other. The present invention also relates to a liquid ejection head incorporating such a piezoelectric actuator unit. For example, the present invention is directed to an ink jet recording head in which pressure fluctuation is caused to ink in pressure generating chambers by the piezoelectric elements to eject ink droplets from nozzle orifices.
It is known an ink jet recording head comprising a piezoelectric actuator unit of longitudinal vibration mode, wherein the piezoelectric elements are extended or shrunk in the axial direction thereof. In such a recording head, an actuation plate constitutes a part of the pressure generating chambers communicated with the nozzle orifices, so that the piezoelectric elements are deformed so as to actuate the actuation plate to generate the pressure fluctuation.
Japanese Patent Publication No. 11-10875A discloses such a piezoelectric actuator unit. As shown in FIGS. 8A and 8B, the piezoelectric actuator unit comprises a actuator array 19 and a fixation board 15 for supporting the actuator array 19. In the actuator array 19, a plurality of piezoelectric elements 14 are arrayed. Each of the piezoelectric elements 14 is a lamination type element in which internal common electrodes 11 and internal segment electrodes 12 are alternately laminated while sandwiching piezoelectric material layers 13 therebetween. The internal common electrodes are exposed to a rear end face of the actuator array 19, and the internal segment electrodes 12 are exposed to a front end face of the actuator array 19. On outer faces of the actuator array 19, there are formed external segment electrodes 16 electrically connected to the internal segment electrodes 12, and an external common electrode 17 electrically connected to the internal common electrodes 11. Terminals of a flexible cable 18 are mounted on contact portions of the external segment electrodes 16 and the external common electrodes 17 by soldering or the like.
Such a piezoelectric actuator unit is generally manufactured as explained below.
First, as shown in FIGS. 9A and 9B, a piezoelectric element formation member 23 is prepared. Specifically, the piezoelectric element formation member 23 is formed by alternately laminating conductive layers 21 to be the internal common electrodes 11 and conductive layers 20 to be the internal segment electrodes 12 while sandwiching piezoelectric material layers 22 therebetween, and then subjected to a drying process and a baking process. More specifically, the conductive layers 21 are exposed to a rear end face of the piezoelectric element formation member 23 and extended to the vicinity of a front end face thereof. On the other hand, the conductive layers 22 are exposed to the front end face of the piezoelectric element formation member 23.
Next, a mask 24 is placed on parts in a top face of the piezoelectric element formation member 23 where are to be boundaries of the external segment electrodes 16 and the external common electrode 17 and where to be dummy actuators (described later) arranged in both side ends of the actuator array 19. The mask 24 is thus generally U-shaped.
Next, as shown in FIGS. 10A and 10B, conductive material is vapor-deposited on outer faces of the piezoelectric element formation member 23 except side faces and a bottom face thereof, to form the external segment electrodes 16 and the external common electrode 17. The mask 24 is removed after the completion of the vapor deposition.
Next, a non-active region of the piezoelectric element formation member 23 in which only the internal common electrodes 11 and the piezoelectric material layers 13 are laminated (see FIG. 10B) is placed on the fixation board 15 made of, for example, metal and fixed thereon by adhesive agent.
After then, slits 25 are formed by cutter such as a dicing saw and a wire saw (not shown) so as to extend from the front end of the piezoelectric element formation member 23 to at least rear ends of the internal common electrodes 12, so that regions to be active regions of the piezoelectric elements 14 are pectinated. Incidentally, at the both side ends of the pectinated piezoelectric elements 14, a pair of dummy actuators having a larger width than that of each piezoelectric element 14 are formed.
In the above method, the external segment electrodes 16 and the external common electrode 17 are finished by executing a single vapor deposition process under such a condition that the mask 24 is provided on their boundaries. The external segment electrodes 16 and the external common electrode 17 must be electrically insulated because the piezoelectric action cannot be performed if both electrodes are electrically connected.
Recently, in view of the cost problem or the like, it is a trend that a portion which is not directly involved with the piezoelectric action is so designed as to have a smaller dimension. That is, the mask 24 is subjected to such downsizing. In such a case, the width of the mask 24 is narrowed and the stiffness thereof is lowered. Accordingly, the downsized mask 24 is likely to be flexed during the vapor deposition, so that a gap is formed between the surface of the piezoelectric element formation member 23 and the mask 24. If the conductive material enters the gap, the external segment electrodes 16 and the external common electrode 17 are electrically connected in the worst case. Such a gap is likely to be formed at a center portion of the mask 24 in the arrayed direction of the piezoelectric elements 14.
In the piezoelectric actuator unit, the contact portions of the external common electrode 17 with respect to the terminal of the flexible cable 18 are arranged at regions which are outer than the region where the external segment electrodes 16 are formed in the arrayed direction of the piezoelectric elements 14, because the contact portions must be arranged so as to avoid the wirings connected to the external segment electrodes 16. For this reason, it is not necessary to make the width of the external common electrode 17 uniform entirely as shown in FIG. 10A only if the contact portions for the flexible cable 18 are secured. In other words, the external common electrode 17 is formed even in unnecessary portions. Further, severe tolerance is imparted to a part the mask 24 corresponding to such an unnecessary portion.
These problems may occur not only in ink jet recording heads, but also similarly occur in other liquid ejection heads for ejecting liquid other than ink.